Rotor and rotor shaft for molten metal

ABSTRACT

A molten metal rotor receives and retains an end of a molten metal rotor shaft. The rotor shaft has one or more projections at the end received in the rotor. The rotor has an inner cavity, a top surface with an opening leading to the inner cavity, and at least one abutment. The opening includes one or more portions for allowing each projection to pass through the opening and into the inner cavity. The rotor and/or shaft are then rotated so at least one of the outwardly-extending projections is under the top surface of the rotor and is against an abutment. A molten metal pump, rotary degasser scrap melter or other device used in molten metal may utilize a rotor/shaft combination as disclosed herein.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of and claims priority to U.S. patent application Ser. No. 14/791,166 entitled Rotor and Rotor Shaft for Molten Metal, filed Jul. 2, 2015, which is a non-provisional of and claims priority to U.S. Provisional Application Ser. No. 62/020,332 entitled “Coupling and Rotor Shaft for Molten Metal Devices, filed on Jul. 2, 2014, the contents of each of the aforementioned applications are incorporated herein in their entirety for all purposes.

FIELD OF THE INVENTION

The inventions herein relate to devices used in molten metal environments and include (1) a rotor, and (2) a rotor shaft to be connected to the rotor.

BACKGROUND OF THE INVENTION

As used herein, the term “molten metal” means any metal or combination of metals in liquid form, such as aluminum, copper, iron, zinc and alloys thereof. The term “gas” means any gas or combination of gases, including argon, nitrogen, chlorine, fluorine, freon, and helium, that are released into molten metal.

Known molten-metal pumps include a pump base (also called a housing or casing), one or more inlets (an inlet being an opening in the housing to allow molten metal to enter a pump chamber), a pump chamber, which is an open area formed within the housing, and a discharge, which is a channel or conduit of any structure or type communicating with the pump chamber (in an axial pump the chamber and discharge may be the same structure or different areas of the same structure) leading from the pump chamber to an outlet, which is an opening formed in the exterior of the housing through which molten metal exits the casing. An impeller, also called a rotor, is mounted in the pump chamber and is connected to a drive system. The drive system is typically an impeller shaft connected to one end of a drive shaft, the other end of the drive shaft being connected to a motor. Often, the impeller shaft is comprised of graphite, the motor shaft is comprised of steel, and the two are connected by a coupling. As the motor turns the drive shaft, the drive shaft turns the impeller and the impeller pushes molten metal out of the pump chamber, through the discharge, out of the outlet and into the molten metal bath. Most molten metal pumps are gravity fed, wherein gravity forces molten metal through the inlet and into the pump chamber as the impeller pushes molten metal out of the pump chamber.

This application incorporates by reference the portions of the following publications that are not inconsistent with this disclosure: U.S. Pat. No. 4,598,899, issued Jul. 8, 1986, to Paul V. Cooper, U.S. Pat. No. 5,203,681, issued Apr. 20, 1993, to Paul V. Cooper, U.S. Pat. No. 5,308,045, issued May 3, 1994, by Paul V. Cooper, U.S. Pat. No. 5,662,725, issued Sep. 2, 1997, by Paul V. Cooper, U.S. Pat. No. 5,678,807, issued Oct. 21, 1997, by Paul V. Cooper, U.S. Pat. No. 6,027,685, issued Feb. 22, 2000, by Paul V. Cooper, U.S. Pat. No. 6,123,523, issued Sep. 26, 2000, by Paul V. Cooper, U.S. Pat. No. 6,303,074, issued Oct. 16, 2001, by Paul V. Cooper, U.S. Pat. No. 6,689,310, issued Feb. 10, 2004, by Paul V. Cooper, U.S. Pat. No. 6,723,276, issued Apr. 20, 2004, by Paul V. Cooper, U.S. Pat. No. 7,402,276, issued Jul. 22, 2008, by Paul V. Cooper, U.S. Pat. No. 7,507,367, issued Mar. 24, 2009, by Paul V. Cooper, U.S. Pat. No. 7,906,068, issued Mar. 15, 2011, by Paul V. Cooper, U.S. Pat. No. 8,075,837, issued Dec. 13, 2011, by Paul V. Cooper, U.S. Pat. No. 8,110,141, issued Feb. 7, 2012, by Paul V. Cooper, U.S. Pat. No. 8,178,037, issued May 15, 2012, by Paul V. Cooper, U.S. Pat. No. 8,361,379, issued Jan. 29, 2013, by Paul V. Cooper, U.S. Pat. No. 8,366,993, issued Feb. 5, 2013, by Paul V. Cooper, U.S. Pat. No. 8,409,495, issued Apr. 2, 2013, by Paul V. Cooper, U.S. Pat. No. 8,440,135, issued May 15, 2013, by Paul V. Cooper, U.S. Pat. No. 8,444,911, issued May 21, 2013, by Paul V. Cooper, U.S. Pat. No. 8,475,708, issued Jul. 2, 2013, by Paul V. Cooper, U.S. patent application Ser. No. 12/895,796, filed Sep. 30, 2010, by Paul V. Cooper, U.S. patent application Ser. No. 12/877,988, filed Sep. 8, 2010, by Paul V. Cooper, U.S. patent application Ser. No. 12/853,238, filed Aug. 9, 2010, by Paul V. Cooper, U.S. patent application Ser. No. 12/880,027, filed Sep. 10, 2010, by Paul V. Cooper, U.S. patent application Ser. No. 13/752,312, filed Jan. 28, 2013, by Paul V. Cooper, U.S. patent application Ser. No. 13/756,468, filed Jan. 31, 2013, by Paul V. Cooper, U.S. patent application Ser. No. 13/791,889, filed Mar. 8, 2013, by Paul V. Cooper, U.S. patent application Ser. No. 13/791,952, filed Mar. 9, 2013, by Paul V. Cooper, U.S. patent application Ser. No. 13/841,594, filed Mar. 15, 2013, by Paul V. Cooper, and U.S. patent application Ser. No. 14/027,237, filed Sep. 15, 2013, by Paul V. Cooper.

Three basic types of pumps for pumping molten metal, such as molten aluminum, are utilized: circulation pumps, transfer pumps and gas-release pumps. Circulation pumps are used to circulate the molten metal within a bath, thereby generally equalizing the temperature of the molten metal. Most often, circulation pumps are used in a reverbatory furnace having an external well. The well is usually an extension of the charging well where scrap metal is charged (i.e., added).

Transfer pumps are generally used to transfer molten metal from the one structure to another structure such as a ladle or another furnace.

Gas-release pumps, such as gas-injection pumps, circulate molten metal while introducing a gas into the molten metal. In the purification of molten metals, particularly aluminum, it is frequently desired to remove dissolved gases such as hydrogen, or dissolved metals, such as magnesium. As is known by those skilled in the art, the removing of dissolved gas is known as “degassing” while the removal of magnesium is known as “demagging.” Gas-release pumps may be used for either of these purposes or for any other application for which it is desirable to introduce gas into molten metal.

Gas-release pumps generally include a gas-transfer conduit having a first end that is connected to a gas source and a second end submerged in the molten metal bath. Gas is introduced into the first end and is released from the second end into the molten metal. The gas may be released downstream of the pump chamber into either the pump discharge or a metal-transfer conduit extending from the discharge, or into a stream of molten metal exiting either the discharge or the metal-transfer conduit. Alternatively, gas may be released into the pump chamber or upstream of the pump chamber at a position where molten metal enters the pump chamber.

Molten metal pump casings and rotors often employ a bearing system comprising ceramic rings wherein there are one or more rings on the rotor that align with rings in the pump chamber (such as rings at the inlet and outlet) when the rotor is placed in the pump chamber. The purpose of the bearing system is to reduce damage to the soft, graphite components, particularly the rotor and pump base, during pump operation.

Numerous rotor shaft to motor shaft couplings are known. A problem with the couplings, however, is that by applying driving force to the rotor shaft the rotor shaft tends to break at the location where the force is being applied. This is typically at the location where the coupling and rotor shaft are in contact, and the broken end of the rotor shaft must often be chiseled out of an opening in the coupling in which it is retained.

Generally, a degasser (also called a rotary degasser) includes (1) an impeller shaft having a first end, a second end and a passage for transferring gas, (2) an impeller, and (3) a drive source for rotating the impeller shaft and the impeller. The first end of the impeller shaft is connected to the drive source and to a gas source and the second end is connected to the connector of the impeller.

The materials forming the components that contact the molten metal bath should remain relatively stable in the bath. Structural refractory materials, such as graphite or ceramics, that are resistant to disintegration by corrosive attack from the molten metal may be used. As used herein “ceramics” or “ceramic” refers to any oxidized metal (including silicon) or carbon-based material, excluding graphite, capable of being used in the environment of a molten metal bath. “Graphite” means any type of graphite, whether or not chemically treated. Graphite is particularly suitable for being formed into pump components because it is (a) soft and relatively easy to machine, (b) not as brittle as ceramics and less prone to breakage, and (c) less expensive than ceramics.

Generally a scrap melter includes an impeller affixed to an end of a drive shaft, and a drive source attached to the other end of the drive shaft for rotating the shaft and the impeller. The movement of the impeller draws molten metal and scrap metal downward into the molten metal bath in order to melt the scrap. A circulation pump may be used in conjunction with the scrap melter to circulate the molten metal in order to maintain a relatively constant temperature within the molten metal.

Rotors are used in molten metal processing for a variety of purposes, such as in a pumping device to circulate molten metal, in a rotary degasser to circulate molten metal and mix gas therewith, and in scrap melters to help create a downward draw to pull scrap into the molten metal where the scrap is melted. The most common type of connection between a rotor shaft and a rotor is to: (1) thread an end of the rotor shaft, (2) bore a threaded opening into the rotor, and (3) then screw the threaded end of the rotor shaft into the threaded opening of the rotor. Problems with this type of connection are that the threads can fail over time, thereby causing the rotor to move erratically and fail, and it is difficult to reverse the threaded end of the shaft to remove the rotor. Thus, if the rotor or rotor shaft fail, often both components must be replaced.

SUMMARY OF THE INVENTION

The present invention alleviates these problems by providing a rotor that includes a section for connecting to a rotor shaft. The connecting section of the rotor has a cavity, an upper surface, and an opening in the upper surface, the opening leading to the cavity. The opening has at least one elongated section. The rotor shaft has an outer surface and a second end with at least one projection extending therefrom, the second end configured to fit through the opening in the upper surface of the rotor (with the at least one projection passing through the at least one elongated section). Once the second end of the rotor shaft is received in the cavity of the rotor, the rotor and/or rotor shaft are rotated so the at least one projection is retained in a position under the top surface and next to an abutment. As the rotor shaft turns the projection presses against the abutment to transmit driving force to the rotor.

In one preferred embodiment the rotor shaft has three or four projections, the opening in the upper surface has the same number of elongated sections that respectively align with each of the projections. The second end of the rotor shaft passes through the opening and into the cavity and is then rotated so each projection is positioned against a respective abutment and under the upper surface of the rotor.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a perspective view of a pump for pumping molten metal, which includes a rotor and rotor shaft according to aspects of the invention.

FIG. 2 is a perspective view of a rotary degasser that may include a rotor shaft and rotor according to aspects of the invention.

FIG. 3 is a perspective view of a scrap melter that may include a rotor shaft and rotor according to aspects of the invention.

FIG. 4 is a side view of a rotor shaft according to aspects of the invention.

FIG. 5 is a view of the rotor shaft of FIG. 4.

FIG. 6 is a top view of a rotor according to aspects of the invention.

FIG. 7 is a side, cross-sectional view of the rotor of FIG. 6 taken along lines A-A.

FIG. 8 is a top view of the rotor of FIG. 6 with the top surface removed.

FIG. 9 is a side, perspective view of a rotor according to aspects of the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring now to the drawing where the purpose is to illustrate and describe embodiments of the invention, and not to limit same, FIG. 1 shows a molten metal pump 20 that includes a rotor shaft 44 and rotor 100 in accordance with aspects of the present invention. During use, pump 20 is usually positioned in a molten metal bath B in a pump well, which may be part of the open well of a reverbatory furnace.

FIG. 2 shows an example of a rotary degasser that could potentially use a rotor shaft/rotor connection in accordance with aspects of the invention and FIG. 3 shows an example of a scrap melter that could potentially use a rotor shaft/rotor connection in accordance with aspects of the invention. Rotor shaft 44′ of rotary degasser 200 is in all respects the same as rotor shaft 44 described below with respect to the way in which it couples to rotor 300.

The components of pump 20, including rotor 100, that are exposed to the molten metal are preferably formed of structural refractory materials, which are resistant to degradation in the molten metal. Carbonaceous refractory materials, such as carbon of a dense or structural type, including graphite, graphitized carbon, clay-bonded graphite, carbon-bonded graphite, or the like have all been found to be most suitable because of cost and ease of machining. Such components may be made by mixing ground graphite with a fine clay binder, forming the non-coated component and baking, and may be glazed or unglazed. In addition, components made of carbonaceous refractory materials may be treated with one or more chemicals to make the components more resistant to oxidation. Oxidation and erosion treatments for graphite parts are practiced commercially, and graphite so treated can be obtained from sources known to those skilled in the art.

Pump 20 can be any structure or device for pumping or otherwise conveying molten metal, such as the pump disclosed in U.S. Pat. No. 5,203,681 to Cooper, or an axial pump having an axial, rather than tangential, discharge. One preferred pump 20 has a pump base 24 for being submersed in a molten metal bath. In this embodiment, pump base 24 preferably includes a generally nonvolute pump chamber 26, such as a cylindrical pump chamber or what has been called a “cut” volute, although pump base 24 may have any shape pump chamber suitable of being used, including a volute-shaped chamber. Chamber 26 may have only one opening, either in its top or bottom, since only one opening is required to introduce molten metal into pump chamber 26, although chamber 26 may have an opening in both its top and bottom. Generally, pump chamber 24 has two coaxial openings of the same diameter and usually one is blocked by a flow blocking plate mounted on the bottom of, or formed as part of, rotor 100. Base 24 further includes a tangential discharge 30 (although another type of discharge, such as an axial discharge may be used) in fluid communication with chamber 26.

The invention is not limited to any particular type or configuration of base, or of even having a base. A pump used with the invention could be of any size, design or configuration suitable for utilizing a rotor shaft and rotor according to the invention.

In the preferred embodiment, post clamps 35 secure posts 34 to superstructure 36. In the embodiment shown, one or more support posts 34 connect base 24 to a superstructure 36 of pump 20 thus supporting superstructure 36, although any structure or structures capable of supporting superstructure 36 may be used. Additionally, pump 20 could be constructed so there is no physical connection between the base and the superstructure, wherein the superstructure is independently supported. The motor, drive shaft and rotor could be suspended without a superstructure, wherein they are supported, directly or indirectly, to a structure independent of a pump base.

A motor 40, which can be any structure, system or device suitable for powering pump 20, but is preferably an electric or pneumatic motor, as shown is positioned on superstructure 36 and is connected to an end of a drive shaft 42. Drive shaft 42 can be any structure suitable for rotating a rotor (also called an impeller), and preferably comprises a motor shaft (not shown) coupled to rotor shaft 44. The motor shaft has a first end and a second end, wherein the first end of the motor shaft connects to motor 40 and the second end of the motor shaft connects to a coupling.

Rotor shaft 44 is shown in FIGS. 1, 4 and 5 and has a first end 44A that connects to the coupling and a second end 44B that connects to rotor 100, best seen in FIGS. 6-9. End 44A can connect to a coupling in any suitable manner.

End 44B of rotor shaft 44 has at least one outwardly-extending projection 50, and as shown has four outwardly-extending projections 50 equally radially spaced about the outer surface 52 (which as shown is cylindrical or annular) of rotor shaft 44, although any suitable number of projections may be used. Each projection 50 can be of any suitable size or shape, and at any suitable location on end 44B of rotor shaft 44. In one embodiment each projection 50 is generally rectangular, between ⅜″ and 1½″ wide, between ¾″ and 3″ in length (as measured along the longitudinal axis of rotor shaft 44) and extends outward from rotor shaft 44 by ¼″ to 2½″. Each projection 50 can be integrally formed with or attached to rotor shaft 44. For example, a slot (not shown) may be formed in rotor shaft 44 and a projection 50 could be cemented or otherwise affixed into the slot. Each slot (if used) is preferably about 1/32″ to ¼″ wider and longer than the width and length of the projection 50 that fits therein, and each slot and could be between 3/16″ to 1″ deep in rotor shaft 44. Second end 44B also may include a chamfered portion 54 that assists in positioning the second end 44B into a connective portion 110 in rotor 100. If rotor shaft 44 is used in a rotary degasser, it would preferably have an internal passage (not shown) for the transfer of gas from first end 44A to second end 44B.

One preferred rotor 100, shown in FIGS. 6-9, could be of any shape or size suitable to be used in a molten metal pump, a rotary degasser or scrap melter, respectively, with the present invention being directed to the connection between the rotor shaft and the rotor and the respective structures of the rotor shaft end 44B and rotor connective portion. Rotor 100 is preferably circular in plain view (although it can be of any suitable shape for its intended use) and includes a displacement structure 102, an inlet structure 104, a top surface 106, a bottom surface 108, and a connective portion 110. Rotor 100 could be comprised of a single material, such as graphite or ceramic, or could be comprised of different materials. For example, inlet structure 104 may be comprised of ceramic and the displacement structure 102 may be comprised of graphite, or vice versa. Any part or all of rotor 100 may also include a protective ceramic coating.

Connective portion 110 connects to end 44B of rotor shaft 44. Connective portion 110 preferably includes (1) an upper surface 300, (2) an opening 302 in upper surface 300, the opening 302 as shown in this embodiment being generally circular and having at least one elongated section 304, and as shown, four elongated sections 304, (3) a cavity 306 beneath upper surface 300 and in communication with each elongated portion 304, and (4) at least one abutment 308 within each cavity 306.

The at least one abutment 308 is adjacent to the at least one elongated section 304 and on the rotational downstream side of elongated section 304. In this manner, when shaft 44 is rotated during operation, rotational driving force is transmitted to rotor 100 by the at least one projection 50 pushing against and transmitting force to the at least one abutment 308. Further, the rotation of shaft 44 during operation would not move a projection 50 back into alignment with a corresponding elongated portion 304, which could lead to the rotor 100 and shaft second end 44B separating.

To connect the rotor shaft 44 to rotor 100, end 44B of rotor shaft 44 is moved through opening 302. The rotor shaft 44 and/or rotor 100 are rotated until at least one projection 50 is under upper surface 300 and pressed against an abutment 308. In this manner the rotor shaft 44 is connected to rotor 100 and can provide rotational driving force thereto.

Having thus described different embodiments of the invention, other variations and embodiments that do not depart from the spirit of the invention will become apparent to those skilled in the art. The scope of the present invention is thus not limited to any particular embodiment, but is instead set forth in the appended claims and the legal equivalents thereof. Unless expressly stated in the written description or claims, the steps of any method recited in the claims may be performed in any order capable of yielding the desired product. 

What is claimed is:
 1. A rotor shaft having a first end configured to be received in a coupling and a second end configured to be connected to a rotor, the second end having at least one outwardly-extending projection that is received and retained in a rotor cavity in order to connect the second end to the rotor; and wherein the rotor shaft has an outer surface and the at least one outwardly-extending projection extends outward at least ½″ from the outer surface.
 2. The rotor shaft of claim 1 that is comprised of one or more of the group consisting of: graphite and ceramic.
 3. The rotor shaft of claim 1 wherein the second end has a plurality of outwardly-extending projections.
 4. The rotor shaft of claim 3, wherein the plurality of outwardly-extending projections are spaced equidistant from one another.
 5. The rotor shaft of claim 3 that has three outwardly-extending projections.
 6. The rotor shaft of claim 3, wherein each of the plurality of outwardly-extending projections extends outward at least ½″ from the annular outer surface.
 7. The rotor shaft of claim 1, wherein the at least one outwardly-extending projection comprises ceramic.
 8. The rotor shaft of claim 3, wherein each of the plurality of outwardly-extending projections comprises ceramic.
 9. The rotor shaft of claim 1 that further includes a rotor connected to the second end of the rotor shaft, the rotor having a rotor cavity in which the second end of the rotor shaft is positioned, and a top surface with a rotor opening through which the second end of the rotor shaft passes into the rotor cavity, the rotor opening having at least one elongated section through which the at least one outwardly-extending projection passes, and the rotor cavity including at least one abutment against which the at least one outwardly-extending projection is positioned when the rotor and rotor shaft are rotated relative one another.
 10. The rotor shaft of claim 3 that further includes a rotor connected to the second end of the rotor shaft, the rotor having a rotor cavity in which the second end of the rotor shaft is positioned, and a top surface with a rotor opening, the rotor opening leading to the rotor cavity and having a plurality of elongated sections configured so that a single one of the plurality of outwardly-extending projections passes through a single one of the plurality of elongated sections, and the rotor cavity includes a plurality of abutments, and a single one of the plurality of outwardly-extending projections is positioned against a single one of the plurality of abutments when the rotor and rotor shaft are rotated relative one another.
 11. The rotor shaft of claim 10, wherein the rotor opening includes a plurality of elongated sections.
 12. The rotor shaft of claim 10, wherein the rotor cavity has three abutments.
 13. The rotor shaft of claim 10, wherein rotor opening includes three elongated sections.
 14. The rotor shaft of claim 9, wherein the rotor cavity has a diameter and the rotor opening has a width, the width of the rotor opening being less than the diameter of the rotor cavity.
 15. The rotor shaft of claim 9, wherein the rotor opening has a first width that does not include the at least one elongated section and a second width that includes the at least one elongated section, the first width being less than the second width.
 16. The rotor shaft of claim 15, wherein the rotor cavity has a diameter and the first width and second width are each less than the diameter.
 17. The rotor shaft of claim 9, wherein the top surface of the rotor comprises ceramic.
 18. The rotor shaft of claim 10, wherein the top surface of the rotor comprises ceramic.
 19. A rotor configured to be connected to a second end of a rotor shaft having at least one outwardly-extending projection, the rotor having a rotor cavity configured to connect to the second end of the rotor shaft and a top surface with a rotor opening configured so the second end of the rotor shaft can pass through the opening and be positioned into the rotor cavity, the rotor opening having at least one elongated section configured so the at least one outwardly-extending projection can pass therethrough, and the rotor cavity including at least one abutment against which the at least one outwardly-extending projection is positioned when the rotor and rotor shaft are connected.
 20. The rotor of claim 19, wherein the rotor opening includes a plurality of elongated sections.
 21. The rotor of claim 19, wherein the rotor cavity has three abutments.
 22. The rotor of claim 19, wherein the rotor opening includes three elongated sections.
 23. The rotor of claim 19, wherein the rotor cavity has a diameter and the rotor opening has a width, the width of the rotor opening being less than the diameter of the rotor cavity.
 24. The rotor of claim 19, wherein the rotor opening has a first width that does not include the at least one elongated section and a second width that includes the at least one elongated section, the first width being less than the second width.
 25. The rotor of claim 24, wherein the rotor cavity has a diameter and the first width and second width are each less than the diameter.
 26. The rotor of claim 19, wherein the rotor has a top surface that comprises ceramic.
 27. A molten metal pump comprising: (a) a motor; (b) a motor shaft extending from the motor and having an end; (c) a coupling that couples to the end of the motor shaft; (d) a rotor shaft having a first end that is received in the coupling and a second end connected to a rotor, the second end having at least one outwardly-extending projection that is received and retained in a rotor cavity in order to connect the second end to the rotor; wherein the rotor shaft has an outer surface and the at least one outwardly-extending projection extends outward at least ½″ from the outer surface; and (e) wherein the rotor has a top surface with a rotor opening through which the second end of the rotor shaft passes into the rotor cavity, the rotor opening having at least one elongated section through which the at least one outwardly-extending projection passes, and the rotor cavity including at least one abutment against which the at least one outwardly-extending projection is positioned when the second end of the rotor shaft is in the rotor cavity and the rotor and rotor shaft are rotated relative one another.
 28. A rotary degasser comprising: (a) a motor; (b) a motor shaft extending from the motor and having an end; (c) a coupling that couples to the end of the motor shaft; (d) a rotor shaft having a first end that is received in the coupling and a second end connected to a rotor, the second end having at least one outwardly-extending projection that is received and retained in a rotor cavity in order to connect the second end to the rotor; wherein the rotor shaft has an outer surface and the at least one outwardly-extending projection extends outward at least ½″ from the outer surface; and (e) wherein the rotor has a top surface with a rotor opening through which the second end of the rotor shaft passes into the rotor opening cavity, the rotor opening having at least one elongated section through which the at least one outwardly-extending projection passes, and the rotor cavity including at least one abutment against which the at least one outwardly-extending projection is positioned when the second end of the rotor shaft is in the rotor cavity and the rotor and the rotor shaft are rotated relative one another.
 29. A scrap melter comprising: (a) a motor; (b) a motor shaft extending from the motor and having an end; (c) a coupling that couples to the end of the motor shaft; (d) a rotor shaft having a first end that is received in the coupling and a second end connected to a rotor, the second end having at least one outwardly-extending projection that is received and retained in a rotor cavity in order to connect the second end to the rotor; wherein the rotor shaft has an outer surface and the at least one outwardly-extending projection extends outward at least ½″ from the outer surface; and (e) wherein the rotor has a top surface with a rotor opening through which the second end of the rotor shaft passes into the rotor cavity, the rotor opening having at least one elongated section through which the at least one outwardly-extending projection passes, and the rotor cavity including at least one abutment against which the at least one outwardly-extending projection is positioned when the second end of the rotor shaft is in the rotor cavity and the rotor and the rotor shaft are rotated relative one another. 